The invention disclosed herein relates to position determining devices, systems and methods, particularly to digitizer systems of the type including a tablet having a conductor structure which interacts with a movable element or pointer suchas a stylus or cursor and the like to provide signals, particularly for a computer, representing the position of the movable element relative to the tablet.
Digitizer systems having a conductor structure and a movable element may be of the electromagnetic type in which signals are electromagnetically coupled between electrical conductors in the conductor structure and an electrical conductor such as a coil in the movable element; of the capacitive or electrostatic type in which signals are capacitively coupled between electrical conductors in the conductor structure and an electrical conductor such an electrode in the movable element; of the optical type in which signals are optically coupled between a light emitting or light receiving conductor structure and light receiving or light emitting structure in the movable element, respectively; of the sonic type in which signals are coupled by means of sound waves between a sound emitting or sound receiving conductor structure and sound receiving or sound emitting structure in the movable element, respectively; etc. The terms "conductor structure" and "conductor" as used herein are meant in a broad sense, and such a conductor structure or conductor may receive or conduct signals of an electrical, magnetic, optical, sonic, etc., nature. Similarly, "induced" is meant in a broad sense and means signals present in a conductor by virtue of some form of coupling.
Digitizing systems provide signals, typically for use by computers, representing the location, e.g., coordinates, of the movable element relative to an active area of the conductor structure, the active area simply being that area at the tablet surface in which the digitizing system is active to provide such position-representing signals at a given accuracy, resolution, etc. Outside the active area, the digitizing system may not recognize or not process signals for conversion to position-representing signals, or may simply not be active to generate or receive such signals, etc. Digitizing systems typically include a conductor structure for each coordinate axis. Description below with respect to the conductor structure of one axis of a coordinate system is generally applicable to the conductor structures of the other axis.
Electromagnetic-type digitizer systems are disclosed, for example, in U.S. Pat. Nos. 3,873,770 of Ioannou; 3,904,822 of Kamm et al.; and 4,368,352 of Davis, all of which are assigned to the assignee of this application.
An electrostatic digitizer system is disclosed, for example, in U.S. Pat. No. 4,705,919 of Dhawan.
The conductor structure in those types of systems comprise, for each coordinate axis, a number of conductors each of which is switched to either couple signals received by the conductors from the movable element to common processing circuitry, or to energize the conductors so that signals thereon supplied from a common source may be coupled to the movable element. Thus, a switch is required for each conductor of the conductor structure of each axis. Although the number of conductors that must be switched depends upon a number of factors including desired resolution and tablet size, it is not unusual for a tablet to employ four or more conductors per linear inch per axis, i.e., adjacent conductors are spaced 0.025 inch or less apart. Therefore, a tablet having an active area of only 12 inches by 12 inches may employ 48 or more conductors per axis requiring 48 or more switches per axis. Typically, the switches are embodied in a multiplexer, and six or more 8-input or three or more 16-input multiplexers are employed per axis.
One way to reduce the overall number of switches or multiplexer inputs required for each axis in digitizer systems of the above type while maintaining a given active area and a given conductor spacing, is to traverse the active area for a particular axis a number of times with the same conductor, i.e., run the conductor in a serpentine fashion such that active portions or "runs" of the conductor are run back and forth across the active area interconnected by connecting portions outside the active area. Recent disclosures of serpentine pattern conductor structures may be found, for example, in U.S. Pat. Nos. 4,734,546, issued Mar. 29, 1988, and 4,831,216, issued May 16, 1989, both of Landmeier; and 4,835,347 of Watson, issued May 30, 1989.
Digitizer systems employing serpentine pattern conductor structures are not, however, a recent development. See, for example, U.S. Pat. Nos. 3,466,646 of Lewin, issued Sept. 9, 1969; 3,647,963 of Bailey, issued Mar. 7, 1972, assigned to the assignee of this application; 3,705,956 of Dertouzos, issued Dec. 12, 1972; 3,819,857 of Inokuchi, issued June 25, 1974; 4,029,899 of Gordon issued June 14, 1977; 4,378,465 of Green et al., issued Mar. 29, 1983; and 4,552,991 of Hulls, issued Nov. 12, 1985.
Arranging the conductors in a serpentine pattern so that spaces or regions between conductor runs (or the runs themselves) may be uniquely identified by unique binary numbers, e.g., in a Gray-type code, also is not a new development. See, for example, the '646 Lewin Patent (1969), the '956 Dertouzos Patent (1972) and the '857 Inokuchi Patent (1974).
One approach in digitizer systems employing serpentinetype grid conductors is to successively divide the active area into smaller and smaller regions. Thus, for example, one conductor divides the tablet in a given axis in half, another conductor in quarters, another in eights, etc. With three conductors, a tablet may be divided according to this approach into eights, with four conductors into sixteenths, with five conductors, into thirty-seconds. See, for example, the Inokuchi '857 Patent.
Using the above approach, the conductor that divides the active area in half, for a 12 inch tablet, separates the adjacent active portions or runs of that conductor by six inches. For a 24 inch tablet, the active portions of the conductor dividing the tablet in half are 12 inches apart. To operate with large spaces between conductor active portions while providing unambiguous signals induced in either the grid conductors or the movable element conductor, requires one or more of the following: high signal levels; a large conductor in the movable element; or sensitive processing circuitry.
Another approach is to divide the tablet area into halves, quarters, etc., as above described, but using a plurality of runs of the same conductor in each sub-divided portion of the tablet, rather than only one conductor run per tablet half, tablet quarter, etc. See the Lewin '646 Patent cited above. Since in this approach the individual runs of the same conductor are not widely separated, the digitizer system does not require the higher signal levels, larger movable element conductor or sensitive processing circuitry of the approach discussed above. However, with a given spacing between adjacent conductor runs of all conductors (said given spacing being referred to herein as "basic spacing"), using a number of runs of the same conductor in the same sub-divided tablet portion simply reduces the total number of unique spaces that can be identified with a given number of conductors.
Typically, grid conductor structures for electromagnetic digitizer systems have four or more separate conductors or conductor active portions per inch of active area. Therefore, a tablet having an active area of 12 inches along a particular axis requires at least 48 conductors or conductor active portions. A tablet using serpentine conductor approaches described above then requires six serpentinely run conductors (2.sup.6 =64). Since digital circuits typically are configured to handle data and addresses in 4, 8, 16 or 32 bits, eight conductors and 8-bit multiplexers would be used. Similarly, for larger tablets, more than eight conductors are needed, and a 16-bit multiplexer (or two 8-bit multiplexers) per axis would be used.
However, 8 or 16 conductors arranged in particular conductor patterns as taught in the Lewin '646 Patent results in a pattern having less than the maximum possible number of unique spaces that can be defined with a given basic conductor run spacing and a given number of conductors. On the other hand, using a pattern as taught in the Inokuchi '857 Patent in a large tablet presents the ambiguity problem discussed above caused by large spaces between conductor runs of the conductor that divides the active area in half or in quarters, etc.
In the approach disclosed in the Landmeier '546 Patent cited above, 16 conductors per axis are run in serpentine paths such that the tablet is uniquely divided only into quarters. A coil in the movable element is uniquely locatable within a tablet quarter from unique codes obtained from the signal phases on the 16 conductors. Signal processing then identifies two adjacent conductor active portions between which, or on one of which, the center of the coil is located. Further signal processing then locates the center of the coil as being between, or on one of, the two adjacent conductor active portions. Thus, determining the location of a coil with respect to the grid is a three-step process per axis. See the Landmeier '216 and the Watson '347 for other approaches using serpentine grid conductor structures.
There is however a need for digitizer systems and digitizer conductor (grid) structures which employ a reduced number of connections between the conductor structure and the signal processing circuitry, whose conductor patterns may be determined relatively easily, which locate a movable element with respect to two conductors with simplified processing, and which perform, for example, with acceptable resolution and accuracy.